The present invention relates to the formation of large reinforcing mat structures. More particularly, it relates to the formation of filament reinforcement mat structures having relatively large dimensions and having a relatively large number of strands of filament reinforcement on the order of about 100 or more per inch.
Methods for the formation of filament reinforced structures are disclosed in U.S. patents assigned to the same assignee as the subject application. The preparation of titanium alloy base foils, sheets, and similar articles and of reinforced structures in which silicon carbide fibers are embedded in a titanium base alloy are described in U.S. Pat. Nos. 4,775,547; 4,782,884; 4,786,566; 4,805,294; 4,805,333; and 4,838,337; assigned to the same assignee as the subject application. The texts of these patents are expressly incorporated herein by reference.
Preparation of composites as described in these patents is the subject of intense study inasmuch as the composites have very high strength properties in relation to their weight. One of the properties which is particularly desirable is the high tensile properties imparted to the structures by the high tensile properties of the silicon carbide fibers or filaments. The tensile properties of the structures are related to the rule of mixtures. According to this rule the proportion of the property, such as the tensile property, which is attributed to the filament, as contrasted with the matrix, is determined by the volume percent of the filament present in the structure and by the tensile strength of the filament itself. Similarly, the proportion of the same tensile property which is attributed to the matrix is determined by the volume percent of the matrix present in the structure and the tensile strength of the matrix itself. To achieve high tensile properties in composite structures it is preferred to have a relatively high volume fraction of the filament reinforcement.
Prior to the development of the processes described in the above-referenced patents, such structures were prepared by sandwiching the reinforcing filaments between foils of titanium base alloy and by pressing the stacks of alternate layers of alloy and reinforcing filament until a composite structure was formed.
The structures taught in the above-referenced patents and the methods by which they are formed, generally improved over the earlier practice of forming sandwiches of matrix and reinforcing filament by compression.
Later it was found that while the structures prepared as described in the above-referenced patents have properties which are a great improvement over earlier structures, the attainment of the potentially very high ultimate tensile strength of these structures did not quite attain the tensile strength values theoretically possible. The testing of composites formed according to the methods taught in the above patents has demonstrated that, although modulus values are generally in good agreement with the rule of mixtures predictions, the ultimate tensile strength is usually much lower than predicted by the underlying properties of the individual ingredients to the composite. A number of applications have been filed which are directed toward overcoming the problem of lower than expected tensile properties. These include U.S. Pat. No. 4,978,585, issued Dec. 18, 1990; U.S. Pat. No. 5,017,438, issued May 21, 1991; U.S. Pat. No. 5,201,939, issued Apr. 13, 1993; and 5,045,407, issued Sep. 3, 1991. The texts of these applications are expressly incorporated herein by reference.
As this technology develops and the fiber reinforced composite structures are themselves improved as by some of the commonly owned patented processes referred to above, the structures are being applied to more end uses and specific requirements for the structures which permit their incorporation in such end uses have become more demanding.
One problem which has surfaced relates to producing flat configuration of composites having larger lateral dimensions. Thus, there is a need for a method and apparatus for producing composite plates having longer lateral dimensions greater than 4.times.5 inches while maintaining composite flatness.